Cross-linked Polyurethane Research Articles

Preparation and characterization of cross-linked polyurethane shell microencapsulated phase change materials by interfacial polymerization

A new cross-linked shell microencapsulated phase change materials (MEPCMs) were prepared by interfacial polymerization, and butyl stearate and polyurethane was empolyed as core material and shell material respectively, while polyurethane shell was reacted by isophorone diisocyanate (IPDI), diethylene triamine (DETA) and pentaerythritol. The surface morphology, chemical structure, phase change properties and thermal stability of MEPCMs were investigated by SEM, FTIR, DSC and TGA. The results show that the prepared microcapsules are sphere with smooth and compact surface, and have good thermal storage properties. When pentaerythritol was employed, the thermal stability and compactness of the cross-linked polyurethane shell MEPCMs has been greatly improved compared to that of linear polyurea shell MEPCMs. When the continuous drying time point is at 120°C for 5h, the weight loss of cross-linked MEPCMs was only 4.65%.

Influence of Carbon Nanotubes on the Mechanical Properties of Cross-Linked Polyurethanes

By the methods of electron microscopy, dynamic mechanical analysis, and transmission of ultrasound, we study the principal mechanical characteristics of systems based on cross-linked polyurethanes and carbon nanotubes. It is shown that they exhibit the percolation behavior and, in the region of percolation transition (0.4–1%), their mechanical characteristics undergo abrupt changes. In this case, the decisive influence is exerted by the aggregates of carbon nanotubes. As the percolation threshold is reached, we observe the formation of a branched network of carbon nanotubes and the tensile strength, the modulus of elasticity, and the velocity of ultrasound significantly increase in the investigated materials.

Degradability of cross-linked polyurethanes based on synthetic polyhydroxybutyrate and modified with polylactide

In many areas of application of conventional non-degradable cross-linked polyurethanes (PUR), there is a need for their degradation under the influence of specific environmental factors. It is practiced by incorporation of sensitive to degradation compounds (usually of natural origin) into the polyurethane structure, or by mixing them with polyurethanes. Cross-linked polyurethanes (with 10 and 30%wt amount of synthetic poly([R,S]-3-hydroxybutyrate) (R,S-PHB) in soft segments) and their physical blends with poly([d,l]-lactide) (PDLLA) were investigated and then degraded under hydrolytic (phosphate buffer solution) and oxidative (CoCl2/H2O2) conditions. The rate of degradation was monitored by changes of samples mass, morphology of surface and their thermal properties. Despite the small weight losses of samples, the changes of thermal properties of polymers and topography of their surface indicated that they were susceptible to gradual degradation under oxidative and hydrolytic conditions. Blends of PDLLA and polyurethane with 30 wt% of R,S-PHB in soft segments and PUR/PDLLA blends absorbed morewater and degraded faster than polyurethane with low amount of R,S-PHB.

Preparation and thermal performance of polyurethane/PEG as novel form-stable phase change materials for thermal energy storage

In this study, a series of the cross-linked polyurethane (PU)/PEG4000 blend was synthesized as novel form-stable phase change materials (FSPCMs) for thermal energy storage through a facile and solvent-free synthetic strategy. In the obtained FSPCM, the PU functioned not only as supporting materials but as phase change substance. The PEG in FSPCM acted as phase change substance. The influence of PEG4000 content on the crystalline properties, phase change properties, thermal reliability and stability was extensively studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermal cycling test and thermogravimetric analysis (TG), respectively. Moreover, the chemical and crystalline structure of obtained PU and FSPCM was confirmed by Fourier transform infrared spectroscopy (FTIR) and polarizing microscope (POM). XRD and POM results indicated that the obtained FSPCM has similar crystalline structure to PEG. DSC results showed that FSPCM appears superior phase change properties with the phase change temperature and the latent heat in the range of 27.73–48.94 °C and 72.19–113.4 J g−1, respectively. The thermal cycling test and TG verified the excellent thermal reliability and stability of FSPCM. The obtained FSPCM exhibited great potential in the field of TES such as the solar energy collection system, exterior wall thermal insulation systems and hot water circulation system.

Influence of Irradiation on the Stability of Polyurethane Matrices in Laser Elements

Photo-oxidative degradation of polyurethanes based on hexamethylene diisocyanate with different oligoether components was investigated using IR spectroscopy and dynamic mechanical analysis. The cross-linking density of highly cross-linked polyurethane based on an oligoether triol of molecular mass 500 tended to increase during photo-oxidation. A polyurethane containing esters was more stable than that based on an oligoether diol of similar molecular mass.

In situ polymerisation and characteristic properties of the waterborne graphene oxide/poly(siloxane-urethane)s nanocomposites

In this study, waterborne graphene oxide/poly(siloxane-urethane)s (GO/SWPUs) nanocomposites were in situ synthesised. Therein, siloxane units facilitated the crosslinking of polyurethanes, and GO imparted the nanocomposites with special functions. With increasing GO content, the average particle size, viscosity, and ionic conductivity of the GO/SWPU dispersion increased, but the absolute value of the zeta potential decreased; this was due to ionic interactions between the COO−NH+(C2H5)3 ions of the SWPU and COO−H+ ions of the GO. The surface roughness of the GO/SWPU film was larger as GO content was higher, which was due to a strong interaction between the GO and SWPU phases. Increasing the GO content improved the thermal resistance, dynamic glass transition temperature, and tensile strength of the GO/SWPU film, but adding more than 0.1 wt% GO yielded unfavourable results. Thus, adding GO improved the thermal and mechanical properties of the GO/SWPU nanocomposites, but this improvement was observed only up to a certain GO concentration, possibly because of the agglutination of GO in SWPU. In addition, the surface and volumetric electrical resistivities of the GO/SWPU nanocomposites decreased when the GO content were increased.

Catalyst-Free Thermoset Polyurethane with Permanent Shape Reconfigurability and Highly Tunable Triple-Shape Memory Performance.

Thermoset shape memory polymer (SMP) with dynamic covalent bonds in the network is a new class of SMPs for which the permanent shape can be reconfigured via topological rearrangement (plasticity). Catalyzed transcarbamoylation has recently been established as an effective exchange reaction for plasticity in cross-linked polyurethane networks. However, ensuring the plasticity severely constrains the network design which adversely affects the ability to tune other classical shape memory properties for practical applications. Facing this new challenge, we design an amorphous polyurethane system for which the cross-linking density can be adjusted in a wide range. We discovered that the use of an aromatic diisocyanate in the synthesis of the polyurethanes facilitates achieving plasticity without requiring any catalyst. The overall network design leads to tunable recovery stress and shape memory transition temperatures without sacrificing the plasticity. The versatility of our polyurethane SMP is further reflected in its triple-shape memory performance. We anticipate that our tunable polyurethanes will benefit a variety of potential SMP device applications.

Synthesis and self-healing property of polyurethane modified with three-furyl diol

Highly cross-linked polyurethanes based on Diels–Alder (DA) reaction have high hardness but poor toughness. A modified polyurethane with three-furyl diol (TF) was synthesized innovatively to improve its mechanical properties. Three-furyl diol (TF) and hydroxyl terminated polyurethane IDI-TF were synthesized first. Then the reaction of IDI-TF with xylene bismaleimide (BMI) generates cross-linked polyurethane ITB-PU (its soft segment content is 11.5%). Finally, the properties of the polyurethane ITB-PU were characterized by a series of methods. It can be observed that the DA reaction occurred at 50.33 °C, the r-DA reaction at 69.55 °C. When heated at 80 °C for 6 h, the self-healing efficiency of the ITB-PU was 43.91% known from the tensile test, and cracks on it virtually disappeared seen from polarizing microscope (POM). When heat was preserved for 12 h, the self-healing efficiency can reach 80.02%.

High Purity Limonene Dicarbonate as Versatile Building Block for Sustainable Non-Isocyanate Polyhydroxyurethane Thermosets and Thermoplastics

Oxidation and subsequent catalytic carbonation of limonene, gained from orange peels, afford high purity limonene dicarbonate (LC) as a versatile building block for tailoring linear and cross-linked non-isocyanate polyurethanes (NIPU) from renewable resources. Spectroscopic investigations reveal so far unknown highly colored carbonation byproducts which are successfully removed to yield crystalline LC. Melt-phase polyaddition of a dimer fatty acid based diamine and its diamine-terminated LC-prepolymers with carbonated 1,4-butanediol diglycidyl ether (BDGC) produces 100% bio-based linear NIPU thermoplastics. Side-reactions occurring during polymerization account for decreasing molar mass with increasing LC content. Curing carbonated pentaerythritol glycidyl ether (PGC)/LC blends with 1,5-diaminopentane, gained from lysine, enables tailoring of 100% bio-based NIPU thermosets exhibiting unconventional property profiles. The incorporation of small amounts high purity LC substantially improves NIPU glass tempe...

Surface charge switchable and core cross-linked polyurethane micelles as a reduction-triggered drug delivery system for cancer therapy

The core cross-linked polyurethane micelles with redox sensitive and pH-responsive surface charge switchable properties were prepared by using diisocyanates as crosslinkers and studied as anticancer drug carriers.

Synthesis and characterization of biodegradable poly(ether-ester) urethane acrylates for controlled drug release

Three polyether-ester triblock diols, with various molecular weights, were synthesized from ε-caprolactone and polyethylene glycol and used, with diisocyanates, as soft segments for the preparation of polyurethane acrylate oligomers. The polyurethane acrylates were used to generate cross-linked polyurethane films via UV initiated polymerization with and without cargo incorporation. Degradation experiment indicated that in PBS/H2O2/CoCl2 the films degraded rapidly compared to PBS alone or with lipase. The polyurethane membrane loaded with the antibiotic tetracycline, demonstrated prolonged release over 200h, suggesting that the polymers could be used as an implant coating for controlled drug release.

Preparation and properties of crosslinkable waterborne polyurethane and polyurethane-acrylic hybrid emulsions and their crosslinked polymers

Stable emulsions of crosslinkable waterborne polyurethanes (CWPU) and waterborne polyurethane-acrylic (CWPU/AC) hybrid with various contents of trifunctional monomer (trimethylolpropane, TMP) and acrylic monomers were successfully prepared in this study. This study focused on the effects of crosslinkable TMP and acrylic monomer contents on the stability/average particle size/viscosity of CWPU and CWPU/AC hybrid emulsions, the mechanical/dynamic mechanical thermal properties, surface contact angle/tension and hardness/water swelling of CWPU and CWPU/AC hybrid film materials. The as-polymerized CWPU emulsion containing 0.06 mol (4.11 mol%) of TMP and CWPU/AC hybrid emulsion containing 60 wt% of acrylic monomer were found to be unstable, indicating that these contents were beyond the limit value of the self-emulsifying ability of dimethylol propionic acid (18.26 mol%). By XPS analysis, CWPU and CWPU/AC film samples were found to have silicone/fluorine enriched surface. The tensile strength/modulus/hardness of the film samples increased markedly with increasing crosslinkable TMP/acrylic monomer up to 0.04 mol/50 wt%, respectively. Meanwhile the elongation at break and water swelling % decreased significantly. The water/ethylene glycol contact angles increased/the surface tension decreased significantly with increasing crosslinkable TMP/acrylic monomer contents up to 0.04 mol/50 wt%. Thus, the optimum TMP/acrylic monomer contents were found to be about 0.04 mol/50 wt% to obtain high performance antifouling coating materials.

Radiation Crosslinking of Polyurethanes: Characterization by FTIR, TGA, SEM, XRD, and Raman Spectroscopy

Gamma radiation can be used for enhancing the physical properties of polyurethane (PU). Radiation was used to crosslink a polyurethane at room temperature; four samples of the PU solid film are irradiated at variable four radiation doses 0, 50, 100, and 150 kGy under vacuum conditions. Crosslinking radiation is more common than oxidative degradation and crosslinking is believed to be more efficient in the soft segment of PU. The structure of the PUs is performed by Fourier transform infrared (FTIR-ATR), Thermogravimetric Analysis (TGA-DTG), and X-ray Diffraction (XRD) which have been used to investigate the effect of gamma radiation on the polyurethane (PU). The results showed that the radiation crosslinking of polyurethanes improved the thermal stability and the crystallinity. The microstructure modifications of polyurethane samples have also been studied as a function of the dose using the scanning electron microscope (SEM). The effects of gamma irradiation on the color changes of polyurethane were observed. The irradiated PUs have conjugated structure and are capable of emitting purple fluorescence.

Synthesis and Characterization of Polyurethanes with High Renewable Carbon Content and Tailored Properties

Thermoplastic and cross-linked biobased polyurethanes with a renewable carbon content ranging from 78 to 98% were synthesized and characterized. The macrodiol and the diisocyanate used were derived from renewable source, the first from castor oil and the second from fatty acid. Moreover, the chain extenders employed were derived from corn sugar and polysaccharides. The effect of component molar ratios and chain extender and cross-linker structure on the final properties was analyzed. Thermal analysis revealed that polyurethanes are formed by amorphous and crystalline domains. It was also observed that the crystallinity of the material is related to the molar ratio of the components and also their structure. Besides, mechanical properties and morphology were tightly dependent on the overall crystallinity, allowing the synthesis of biobased polyurethanes with tailored properties and high renewable carbon content.

Lateral cross-linking of polyurethane using isophorone diisocyanate and glycerol to control tensile and shape memory properties

Lateral cross-linking of polyurethane (PU) was used in this study to improve the tensile strength, thermal stability, and shape memory effect of PU. The hard segment in the middle of PU was used as the cross-linking site to attain high tensile stress and reproducible shape recovery without a significant decrease in tensile strain. Specifically, we investigated whether lateral cross-linking of PU using isophorone diisocyanate (IPDI) is feasible by linking the carbamate bonding or glycerol hydroxyl groups of PU. Therefore, the effects of the IPDI cross-linking site and the cross-linker content were examined by comparing the thermal, tensile, and shape memory properties as well as the cross-link density and water swelling with those of unmodified PU.

PIEZORESISTIVE BEHAVIOR OF THE SYSTEMS BASED ON CROSS-LINKED POLYURETHANES AND CARBON NANOTUBES

The research of features of electrical conductivity of the systems based on cross-linked polyurethanes and carbon nanotubes depending on the value of external pressure is done using the method of impedance spectroscopy. It is set that dependence of electrical conductivity on pressure shows a percolation behavior. The mechanisms of nonlinear change of electrical conductivity with growth of pressure is described. It is rotined that the probed systems are perspective piezoresistive materials for creation of the sensors of pressure.

Ageing mechanisms of polyurethane adhesive/steel interfaces

For the achievement of a complete understanding of the ageing and corrosion of adhesively bonded steel substrates, both the ageing of a polyurethane reference adhesive and the simultaneous corrosion of a mild steel substrate were studied by combined spectroscopic, electrochemical and microscopic techniques. A corundum-blasted mild steel was used as metal substrate in combination with a cross-linked reference polyurethane adhesive free from additional additives or fillers. The ageing was performed under full immersion in a chloride-free aerated electrolyte at elevated temperature. A strong influence of the water saturated polymer phase on the change in the interfacial oxide film structure of the metal substrate was observed. The thickening and hydroxylation of the metal oxide film during the corrosive delamination of the polyurethane film indicated that the de-bonding mechanism of the polyurethane adhesive is mainly based on interfacial water enrichment and a thereby induced growth of the interfacial oxide. The measured electrochemical properties of this oxide indicate that it is highly conductive and allows for oxygen reduction as the counter reaction to metal oxidation.

Super‐toughened poly(l‐lactic acid) fabricated via reactive blending and interfacial compatibilization

AbstractSuper‐toughened poly(l‐lactic acid) (PLLA) was prepared by reactive blending of PLLA with poly(ϵ‐caprolactone) (PCL), glycerol and 4,4′‐methylenediphenyl diisocyanate. The reactive interfacial compatibility between PLLA and the formed crosslinked polyurethane (CPU) in the PLLA matrix was studied in detail. The morphology and the toughness of the blends can be tuned by changing the CPU content. The results indicate that the impact strength of PLLA shows a tendency to higher values with the increasing PCL content up to 20 wt%. The notched impact strength of the blend with 20 wt% PCL increases to 55.01 kJ m−2, which is 24.9 times higher than that of neat PLLA. The elongation at break is also increased from 5% to 139.4%, indicating the brittle − ductile transition. The increased interfacial binding strength through the reactive interfacial compatibility and the formation of a CPU network in the PLLA matrix account for the improved toughness of PLLA/CPU blends. Dynamic mechanical analysis results indicate that the compatibility between PLLA and CPU is improved with increasing CPU content resulting in the formation of more interfacial phase. In addition, rheological property measurements indicate that the improvement in storage modulus and complex viscosity is ascribed to the formation of a CPU network in the PLLA matrix. © 2016 Society of Chemical Industry

Effect of a cross-linking agent on the foamability of microcellular injection molded thermoplastic polyurethane

Thermoplastic polyurethane is one of the most versatile thermoplastic materials being used in a myriad of industrial and commercial applications. Thermoplastic polyurethane foams are finding new applications in various industries including furniture, automotive, sportswear, and packaging because of their easy processability and desirable, customizable properties. Low bulk density and a good foam microstructure are important properties that affect the mechanical properties, economics, and performance of the final product. In this study, the effect of a cross-linking agent on the foamability of microcellular injection molded thermoplastic polyurethane was studied with an aim to reduce the bulk density while achieving a consistent microstructure. Gel permeation chromatography showed an increase in the weight average molecular weight by 5.0% with the addition of a cross-linking agent. Rheological studies on the materials showed that the addition of a cross-linking agent increased the storage modulus and viscosity, while reducing the tan δ value. Using microcellular injection molding, cross-linked thermoplastic polyurethane could be foamed to a minimum density of 0.159 g/cc at the higher end of the processing window, as compared with a minimum density of 0.193 g/cc for pure thermoplastic polyurethane foam. Scanning electron microscope analyses of the foamed parts showed a bimodal foam structure for thermoplastic polyurethane with a cross-linking agent and a more integral foam structure with less cell coalescence even at higher density reductions.

Preparation and properties of emulsifier/N‐methylpyrrolidone‐free crosslinkable waterborne polyurethane–acrylate emulsions for footwear adhesives. I. Effect of the acrylic monomer content

ABSTRACTStable emulsions of emulsifier/N‐methylpyrrolidone‐free crosslinkable waterborne polyurethane–acrylates (C‐WBPUAs) with various acrylic monomer contents (0, 10, 20, and 30 wt %) for footwear adhesive materials were successfully prepared in this study. The effects of the acrylic monomer content on the shelf stability, mean particle size, and viscosity of the C‐WBPUA emulsions; the tensile properties and dynamic mechanical thermal properties of the C‐WBPUA film samples; and the adhesive strengths between the upper (synthetic leather) and the sole (ethylene vinyl acetate rubber) in both the dry and wet states of the formulated adhesives (C‐WBPUA emulsion–thickener–hardener) were examined. The adhesive strengths of the formulated adhesives for footwear (leather–sole) in both the dry and wet states increased with increasing acrylic monomer content up to 20 wt %; after this, they almost levelled off. Thus, C‐WBPUA20 and C‐WBPUA30, where the number indicates the acrylic monomer content, can be recommended as high‐performance adhesive materials for footwear. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43758.